Oscillator means for driving a resonant load

ABSTRACT

Improvements in sonic alerting devices of the type controlled by the natural frequency of the transducer are shown as well as improved circuits for driving loads in general. Efficient drive circuits suited for but not limited to integrated circuit chips employ transistors connected in the common collector-common base configuration. Very efficient quasisymmetrical circuits are shown employing cross coupled transistors in place of inefficient resistors. Bridge oscillators are shown in which the transducer controls the frequency of oscillation and in which the voltage driving the transducer is nominally twice the supply voltage. There are circuits made of two sets of elements and each set compels the other to oscillate at opposite phase with additive effect in powering the transducer.

United States Patent Potter Jan. 25, 1972 OSCILLATOR MEANS FOR DRIVING A RESONANT LOAD [72] Inventor: Bronson M. Potter, RFD #1, Greenville,

[22] Filed: May 1, 1969 [21] Appl. No.: 820,890

[52] U.S.Cl. ..340/384 E,331/ll0,33l/l16M [51] Int. Cl. ..G08b 3/00 [58] Field of Search ..340/3 84 R, 384 E; 307/308;

[56] References Cited UNITED STATES PATENTS 3,277,465 10/1966 Potter ..340/384 3,440,648 4/1969 Camenzind.. ..340/388 3,475,698 10/1969 Noe ..331/108 Primary Examiner- Robert L. Richardson Attorney-John Noel Williams [5 7 1 ABSTRACT lmprovements in sonic alerting devices of the type controlled by the natural frequency of the transducer are shown as well as improved circuits for driving loads in general. Efficient drive circuits suited for but not limited to integrated circuit chips employtransistors connected in the common collectorcommon base configuration. Very efficient quasisymmetrical circuits are shown employing cross coupled transistors in place of inefficient resistors.

Bridge oscillators are shown in which the transducer controls the frequency of oscillation and in which the voltage driving the transducer is nominally twice the supply voltage. There are circuits made of two sets of elements and each set compels the other to oscillate at opposite phase with additive effect in powering the transducer.

4 Claims, 6 Drawing Figures PATENTED JAN25 1372 SHEEY 1 0f 2 FIG. la

PATENTED JANZS m2 SHEET E OF 2 FIG. 4

FIG. 3

FIG. 2

,45 Ill FIG. 5

OSCILLATOR MEANS FOR DRIVING A RESONANT LOAD This invention relates to sonic alerting devices and oscillators. Reference is made to applicants prior US. Pat. No. 3,277,465, sold by P. R. Mallory Co., under the mark Sonalert," to applicants prior US. Pat. No. 3,447,151, and to applicants copending patent application Ser. No. 809,539.

An object of the invention is to provide improved inexpensive, high power solid state alerting devices and oscillatory mechanisms with resonant loads.

Another object is to provide such circuits that are highly efficient, have high power output and are not sensitive to variations in the supply voltage and are conveniently manufactured as integrated circuits on single semiconductor chips.

Another object is to provide sonic alerting devices which are suitable for audible warnings for automobile instrument panels, backup warnings, telephones, fire alarms and the like.

According to one aspect of the invention, it is realized that the transducer, connected at one terminal to a configuration of common-base common-collector transistors, can have one terminal connected to common while still being in the oscillatory feedback loop with resultant advantage.

According to another aspect of the invention each terminal of the transducer can be connected to a separate commonbase common-collector configuration of transistors and driven at its series-resonant mode at a peak-to-peak voltage exceeding that of the power supply.

According to another aspect of the invention it is realized that very powerful highly efficient sonic alerts can be achieved employing a piezotransducer in an oscillating bridge type circuit or a circuit comprising two sets of active elements, the two sets and the transducer connected to define two oscillating power source units in which each compels the other to operate substantially in reverse phase and in an additive relation that is synchronized by the natural frequency of the transducer.

This invention features driving stages in which there need not be any resistors in the high current branches of the circuit; two transistors are connected in the same-syntax common-collector common-base mode so that the transducer may both be driven by the emitter of the common collector transistor and control the base-emitter bias of the common base transistor; all of the transistors can be of the same syntax (all NPN or PNP); there can be close spacing of all parts in integrated circuitry; and manufacture is possible according to state-of-theart same-syntax integrated circuit techniques.

Other objects, features and advantages will appear from the following description of preferred embodiments of the invention, taken together with the attached drawings thereof, in which:

FIG. I is a schematic wiring diagram of a preferred embodiment of the invention connected to a piezoelectric transducer alerting device employing a symmetrical circuit giving nominally twice the power supply voltage at the transducer.

FIG. 1A is a diagrammatic representation of the bridge oscillator circuit of FIG. 1;

FIG. 2 is a schematic wiring of a simple and very inexpensive embodiment that can be advantageously manufactured from discrete components;

FIG. 3 is an embodiment similar to that of FIG. 2 but including a third transistor to eliminate a resistor in the high current branch of the circuit and suitable for manufacture as an integrated circuit; and

FIG. 4 is an embodiment similar to that of FIG. 3 but including a divider resistance to provide easier starting over a range of power supply voltages.

FIG. 5 is a schematic wiring diagram similar to FIG. 1, illustrating a typical alternate resonant load.

Referring to FIG. 2, transistor and transistor 12 are coupled in a configuration ll of the common-base common-collector type (in a manner well known per se to the art) through resistor 14. Base 16 of transistor 10 is coupled to the negative supply common 18 through transducer 20. Base 16 of transistor 10 is prevented during oscillation from going more than 0.6 volts negative of emitter 22 by diode 24. By such connection of the common-collector common-base configuration 11 of transistor 12 and transistor 10 respectively, transducer 20 can have one lead 26 connected to common 18. It thus can be driven nominally at the supply voltage peak-to-peak and controls the frequency of oscillation by providing a low-impedance path at its series-resonant frequency between base 16 and common 18.

Referring to FIG. 3 (all numbers the same as in FIG. 2) transistor 28 has been used to replace resistor 14 of FIG. 2. It is advantageously coupled to the oscillating circuit by means of transducer 20 and diode 30. Diode 30 has a low impedance e.g., 10 ohms nominally, so that lead 26 of transducer 20 is still effectively coupled to common 18 when considering the oscillation of configuration 11, yet efiectively switches common-base transistor 28, the base 32 of which is effectively coupled to the supply commons l8 and 38 by means of the low-impedance paths supplied by resistors 34 and 36.

Referring to FIG. 4 (all numbers the same as in FIGS. 2 and 3) resistor 13 has been replaced by thedivider resistors 40 and 42. This reduces the gain of configuration 11 in a manner known to the art to prevent the configuration 11 from becoming strongly monostable or bistable, thus aiding oscillation at low supply voltages.

Referring to FIG. 1 the common-collector common-base configurations 11 and 111 exactly duplicate the configuration of FIG. 4 in operation. It has been stated that lead 26 of transducer 20 must be returned to a low-impedance point with respect to supply common in order for configuration 11 to oscillate. It will become readily apparent to those versed in the art that when lead 26 is driven for example positive through transducer 20, configuration 111 will switch in such a manner that lead 26 is driven negative. This is to say that lead 26 is coupled to supply commons 38 and 18 through a negative impedance, thus satisfying the foregoing criterion for oscillation.

It will be easier for the layman to understand the invention by viewing configuration 11 as regenerating in such a manner that lead 26 is driven positive through transducer 20. This positive pulse can be imagined as turning transistor on. By this means collector 115 of transistor 110 approaches the potential of emitter 122 of transistor 110. Thus base 117. of transistor 112 approaches the potential of emitter 109, turning transistor 112 off." In point of fact, configurations 11 and 111 are image impedances for each other, each supplying the negative low-impedance returns through transducer 20 to commons 38 and 18 for the other.

Transistors 44 and 46 provide advantages over the supplanted resistors in the same manner that transistor 28 in FIG. 3 replaces resistor 14 of FIG. 2. Transistors 44 and 46 are switched in a manner well known to those versed in the art, through resistors 48 and 50.

The embodiment of FIG. 1 may be represented as a bridge oscillator, as shown in diagrammatic form in FIG. 1A. The device can be envisioned as comprised of four switching circuits. Configuration 11 is one switch, configuration lll another, transistor 46 another, and transistor 44 the last. It can be seen that when switching circuits 46 and 111 are on" or closed with switching circuits 11 and 44 off or open, the transducer is driven by the full supply potential in one polar sense, and that when switching circuits 11 and 44 are on with switching circuits 46 and 111 off" the transducer is driven by the full supply potential in the other polar sense. Thus, twice the supply potential is impressed across the transducer during each oscillatory cycle.

Typical operational values of parameters for elements of the circuit of FIG. 1 are as follows:

Resistors 40 and I0 kfl Resistors 42 and 142 I0 kn Resistors 15 and 115 10 kt! Resistors 48 and 50 I0 k0 Resistors 52 and 54 1.5 k!) Diodes Silicon Transistors, l0, 12, 110, 1 12, 33, and 46 h greater than 50.

Transducer 20 2.800 c.p.s. nominal,

e.g., a piezoelectric transducer such as that found in the Sonalert mentioned above.

FIG. 5 illustrates that the bridge circuit shown can be applied to transducers of other kinds. The components are all the same as in FIG. 1 except that in place of the sonic transducer a radio frequency series tuned tank circuit 45 is substituted. Other suitable loads are tuning fork oscillators, piezotransformers, auto horns and other devices in which the impedance at the desired frequency of operation is so much lower than at other frequencies that it provides the commonbase common-collector configuration or configurations with sufficient gain to oscillate.

In summary, the transducer may be any electrically driven device which can be characterized as having a natural or resonant frequency determined by its capacitive and inductive characteristics at which frequency the electrical impedance of driven device is a minimum. Thus the transducer may be viewed as an element that, at a certain frequency, opposes the flow of current less than at any other frequency so that oscillation is maintained at this critical frequency at which the transducer is said to be in its series resonant mode. Such a device is described, for example, in applicant's prior US. Pat. No. 3,447,]51, reference numeral 34; and No. 3,277,465, reference numeral 12; and in applicants copending application Ser. No. 809,539, reference numeral 40; and in Dundon US. Pat. No. 3,331,970.

In the embodiments shown the various oscillating units have been formed by two transistors compound connected with the first connected common collector and the second connected common base. While this specific arrangement is presently preferred from the point of view of small number of active elements and ready adaptability to manufacture with state-ofthe-art skills, other arrangements are within the broader aspects of the invention. Thus that aspect of the invention which requires a common-collector common-base type of configuration is not limited to the pair of transistors mentioned. For instance a larger number of transistors can be combined together to achieve the same essential characteristics as the pair mentioned above, and are within the phrase switching configuration of the common-collector common-base type" as used herein.

The negative impedance characteristics of the common-cob lector common-base configurations are extremely efficient and offer significant advantages in the bridge oscillating circuit described. It will nevertheless be understood according to the general aspect of the invention of powering a piezoelectric sonic transducer with a bridge oscillator to obtain an additive effect, and thus an extremely large output with a given power source, that other types of active devices may be found useful with this concept.

Numerous variations in the specific details are within the spirit and scope of the invention.

I claim:

1. In an electronic circuit, capable when connected to a power supply of driving a resonant load through a pair of leads, at a frequency determined by the natural frequency of the load, the improvement wherein there are two switching configurations of the common-collector common-base type,

one connected to each lead of the resonant load, each said configuration comprising first and second transistors each having a base, a collector and an emitter, the emitters of said first and second transistors being connected together, the collector of the first transistor being connected to the base of the second transistor, and the base of the first transistor being connected to the respective lead of the resonant load, each said configuration adapted to oscillate at a frequency determined by the natural frequency of the load and each configuration respectively adapted to impress a voltage upon the respective lead of the resonant load, the configurations thus connected having the characteristic of oscillatin nominall out of phase with respect to each other where y an oscr latory voltage can be impressed on said resonant load substantially greater than the power supply voltage.

2. The electronic circuit of claim 1 including two additional active devices, one coupled respectively to each of the said common-collector common-base configurations, each active device arranged to be switched by said load at the natural frequency of the load.

3. The electronic circuit of claim 2 in which each of said active devices comprises a transistor, each acting as a switched load for one of the common-collector common-base configurations, thereby to inexpensively improve the economy of operation of said circuit.

4. The electronic circuit of claim 1 in which said resonant load is a piezoelectric sound-emitting transducer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.

I t fl Bronson M. Potter It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 3, after "driving" insert -resonant--.

Signed and sealed this 15th day 9;: August 1972.

('S-EAL) Attest! I EDWARD M. FLETCHER, JR. ROBERT GOTTSCHALK Commissioner of Patents Attesting Officer USCOMM-DC 037O-P6B ".5. GOVIINMINT PRINYWG OFFICE 1 I0. n-JIl-"l FORM PO-OSO (O-69) 

1. In an electronic circuit, capable when connected to a power supply of driving a resonant load through a pair of leads, at a frequency determined by the natural frequency of the load, the improvement wherein there are two switching configurations of the common-collector common-base type, one connected to each lead of the resonant load, each said configuration comprising first and second transistors each having a base, a collector and an emitter, the emitters of said first and second transistors being connected together, the collector of the first transistor being connected to the base of the second transistor, and the base of the first transistor being connected to the respective lead of the resonant load, each said configuration adapted to oscillate at a frequency determined by the natural frequency of the load and each configuration respectively adapted to impress a voltage upon the respective lead of the resonant load, the configurations thus connected having the characteristic of oscillating nominally 180* out of phase with respect to each other whereby an oscillatory voltage can be impressed on said resonant load substantially greater than the power supply voltage.
 2. The electronic circuit of claim 1 including two additional active devices, one coupled respectively to each of the said common-collector common-base configurations, each active device arranged to be switched by said load at the natural frequency of the load.
 3. The electronic circuit of claim 2 in which each of said active devices comprises a transistor, each acting as a switched load for one of the common-collector common-base configurations, thereby to inexpensively improve the economy of operation of said circuit.
 4. The electronic circuit of claim 1 in which said resonant load is a piezoelectric sound-emitting transducer. 